Must have software for shell users of OS X

iTerm allows the user access to additional features not provided by the pre-installed Terminal program. Such as custom backgrounds, saved settings, middle mouse click copying, and other features available in Linux shells.

I've also found programs from MacPorts (or similar packages) to be quite useful when I need things done very fast. For example ncftp, unrar, and par2. There is also a problem with finding 7zip for the Mac. This can be installed from MacPorts.

Some people advocate gedit (a cross-platform text/program editor). I personally like Text Wrangler.